Sawdust ingestion by the tropical shad (Tenualosa macrura, Teleostei: Clupeidae): implications for conservation and fisheries Original Research Article

Tenualosa macrura is the main target species of a gillnet fishery in the coastal waters of the Bengkalis region, Indonesia, where it has a strong cultural significance. However, in recent decades, the fishery has declined markedly. The stomach contents of 1255 fish were dominated by sawdust (by weight), and only 26% of the diet comprised planktonic Crustacea. Carbon isotope analyses showed that the δ13C signature of this sawdust matched the δ13C signature of old-growth hardwood timber. Plankton samples from the waters where these fish were caught had high concentrations of sawdust, and 25 sawmills were mapped along the banks of waterways that drained into these coastal waters. Sawdust has no, or very little nutritional value for T. macrura or other species of planktivorous fish, and can only have a negative impact on their health and survival. However, the impact would depend on how much of its life cycle is spent in these coastal waters. We calculate that T. macrura spends between 2.2 and 33% of its adult life in these sawdust-rich waters. Although overfishing may be the main cause of the decline in this fishery, we propose that sawdust pollution may also contribute significantly, threatening the survival of this and possibly other planktivorous fishes in this region.